Imaging agents that activate under specific conditions, for example under low pH or in the presence of an enzyme, have the ability to provide molecular, biological, and physiologically specific contrast. Most often, these activatable probes are optical in nature, wherein an emitter is linked with a quencher by a cleavable domain. This has allowed for the characterization and imaging of not just binding events, but other biological processes such as enzyme activity. The activatable optical contrast agents, however, are hampered by their poor tissue penetration, which has limited their clinical translatability in many areas. Therefore, a nuclear activatable alternative is highly desired in order to fulfill the promise of this class of imaging agent.